The present invention relates to a laser diode including a substrate-side protection layer and, more particularly, to the inclusion of a dielectric barrier region on the substrate side of a semiconductor laser diode to reduce facet degradation and improve facet coating, as well as the environmental durability of the laser structure.
Conventional semiconductor laser diodes and superluminant diodes comprise an epitaxial layer grown over a substrate. In most conventional arrangements, the substrate is of N-type conductivity and the epitaxial is of P-type conductivity, although a complementary structure may also be formed. The diode device, while still in wafer form, is cleaved to form laser bars that include front and rear facets. These facets are subsequently coated to define the cavity of the diode. A dielectric layer is deposited over the epitaxial side of the device to ensure that current from the contact pad is injected into only the active stripe formed within the structure.
In forming the final device, the front and rear facets are coated (with either a high reflectivity (HR) coating or an anti-reflective (AR) coating, as appropriate). As currently processed, there may be vulnerable points in the integrity of the facet coating that result from contamination and oxidation present along the edge where the facet, or face, meets the substrate surface. As a result, the facet coating can be poorly anchored at the substrate edge and may, under certain circumstances, result in degradation of the facet/coating interface. Further, once the degradation process begins, the facet coating may begin to delaminate, eventually resulting in failure of the device, or the system containing the device.
Thus, a need remains in the art for a method of eliminating diode device failure associated with substrate-side contamination effects.